Correlated double sampled (cds) pixel sense amplifier

ABSTRACT

A correlated double sampled (CDS) pixel is provided. The CDS pixel comprises an image sensing device, an inverting amplifier, a capacitor, and first and second switches. The image sensing device generates charge based on image content. The inverting amplifier is in operable communication with the image sensing device. The capacitor is configured as a feedback to the inverting amplifier, wherein the first capacitor configured as a switching capacitor and configured to integrate an image signal received by the image sensing device. The first switch is in operable communication with the inverting amplifier and is configured to control sample timing of a correlated offset signal. The second switch is in operable communication with the image sensing device and is configured to control sample timing of the image signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application filed on Jan. 13, 2014, having Ser. No. 61/926,442 and attorney docket number INTRI-030PUSP, by Eugene M. Petilli, entitled “A Correlated Double Sampled (CDS) Pixel Sense Amplifier,” which is hereby incorporated by reference in its entirety.

It is envisioned that the embodiments described herein also could be combined with some or all of the technologies described in the commonly assigned U.S. Pat. No. 7,215,270, entitled “Sigma-Delta Modulator having selectable OSR with Optimal Resonator Coefficient,”; U.S. Pat. No. 7,576,671, entitled “Mismatch-shaping Dynamic Element Matching Systems and Methods for Multi-bit Sigma-delta Data Converters,”; U.S. Pat. No. 7,605,652, entitled “Sigma-delta Based Class D Audio Power Amplifier with High Power Efficiency,”; U.S. Pat. No. 7,612,608, entitled “Sigma-delta Based Class D Audio or Servo Power Amplifier with Load Noise Shaping,”; U.S. Pat. No. 7,860,189, entitled “Hybrid Heterodyne Transmitters and Receivers,” U.S. Pat. No. 8,379,760, entitled “Hybrid Heterodyne Transmitters and Receivers,” U.S. Patent Publication US-2012-0218445-A1, entitled “Imager Readout Architecture Utilizing A/D Converters,” the provisional patent application entitled Foveal Imager Readout Integrated Circuit (ROIC), application Ser. No. 61/879,276, by Eugene M. Petilli, filed on Sep. 18, 2013 and converted to a nonprovisional patent application having Ser. No. 14/490,448 and attorney docket number INTRI-028AUS on Sep. 18, 2014; and, and the provisional patent application entitled “Stacked Photodiode Multispectral Imager, application Ser. No. 61/902,912, by Eugene M. Petilli, filed on Nov. 12, 2013 and converted to a nonprovisional patent application having Ser. No. 14/539,607 and attorney docket number INTRI-029AUS on Nov. 12, 2014. The contents of each of these above-listed patents and patent applications are hereby incorporated by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable

FIELD

At least some embodiments described herein generally relate to devices, systems, and methods for interfacing to image sensing elements. More particularly, at least some embodiments relate to devices, systems and methods that use charge to represent image intensity and convert the charge into Converter.

BACKGROUND

Conventional photodiode based imagers such as Active Pixel or CMOS Sensors utilize a photodiode and a three (3T) or four transistor (4T) sense amplifier per pixel architecture to provide a low impedance representation of the intensity of light that illuminated the photodiode. This picture element, or pixel, is replicated into an X by Y array of pixels which forms a Focal Plane Array.

The PN junction of the photodiode (PD) has a parasitic capacitance, which varies with the reverse bias voltage across the PD. The PD is often P-I-N (pinned); that is, the depletion of the PD is designed to deplete or drain out all charge out of the collection region, at a certain voltage. Pinning the PD helps to optimize the quantum efficiency, capacitance and linearity of the PD. FIG. 1 is a diagram of a standard four transistor (4T) pixel 10, as is known in the prior art, and includes a pinned PD 12, a transfer gate (TG) transistor 14 (designed as M_(TG)), a storage capacitor 16, a source follower transistor M_(SF) 24, a select transistor MSEL 18, and a RESET transistor M_(RST) 20 that is responsive to a RESET signal 21. Referring to FIG. 1, first, a Reset Phase, controlled by the Reset transistor 20, is used to clear any previous charge on the PD 12. Then, the voltage across the PD 12 (and Floating Diffusion node, FD-X capacitor 16) is initialized to a known reverse bias during a Reset Phase, controlled by turning on both the TX (transfer gate) transistor 14 and RESET transistor 20.

During an Integration Phase, the TX transistor 14 is opened, disconnecting the bias source (VRESET 26) from the PD 12, leaving the initial charge stored on the parasitic PD capacitor. When a photon hits the PD 12, it is converted into some number of electrons, each with a charge of one electron volt. The charge is accumulated in the parasitic capacitance, which changes the voltage. The time during which the charge is allowed to accumulate is referred to as the integration time.

During a Transfer Gate (TG) phase, controlled by the TX transistor 14, the charge accumulated on the PD 12 is moved from the PD 12 to a storage capacitor 16, which is often fabricated from a Floating Diffusion (FD)—represented by the X-FD 16 in FIG. 1. The voltage across the FD 16 is presented to the source node of a MOS device 22 which is connected as a non-inverting common drain amplifier referred to as the Source Follower (SF) 22. The SF 22 provides power gain by transforming the high impedance charge into a low impedance voltage output. There is a series SELECT transistor 18 which enables the SF 22 to drive an output bus (not shown in FIG. 1, but which is in operable communication with the row 30 and column 32 that receive respective select signals SELECT_1 and SELECT_2), which are shared with other pixels typically from the same column. At the end of the column bus 32 is a current sink (not shown) which biases the one source follower 22 that is selected. For example, in one embodiment, the source of the SELECT transistor 18 is connected to a column-based output bus 32. The SELECT_(—)1 signal selects which of the N rows places its voltage on the M column buses 32. Normally, only one row is enabled at a time. This configuration is sometimes referred to as a Wired-OR, tri-state, or one-hot bus.

The output or column bus 32 can be used to drive a Correlated Double Sampling (CDS) amplifier (not shown in FIG. 1) which is used to remove the spatial error created by the offset variations and 1/f noise of the multiple SFs 22 that are sequentially driving the output bus 32. The output of the SF 22 is sampled first after the Reset phase (but before the TG phase) to store the “residual” offset from the reset. A second sample is taken after the TG phase to store the signal plus offset and noise. The stored offset and signal voltages are subtracted (correlated) to remove the error sources, leaving only the signal, which represents the light intensity.

SUMMARY

The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the disclosed embodiments. This summary is not an extensive overview of the embodiments described herein, and is neither intended to identify key or critical elements of these embodiments, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the disclosed embodiments in a simplified form as a prelude to the more detailed description that is presented later.

In addition, at least some of the embodiments described herein are is intended to be usable with many different types of systems that use photodiodes, including imaging systems, especially those that are based on sigma-delta modulators (SDM), as well as many different types of sensing systems, amplifiers, etc.

In one embodiment, a Correlated Double Sampled (CDS) pixel is provided, the CDS pixel comprising an image sensing device, and inverting amplifier, a first capacitor, a first switch, and a second switch. The image sensing device generates charge based on image content. The inverting amplifier is in operable communication with an output of the image sensing device, where the inverting amplifier comprises an inverting input and an amplifier output. The first is configured as a feedback to the inverting input of the inverting amplifier, where the first capacitor is configured as a switching capacitor and is configured to integrate an image signal received by the image sensing device. The first switch is in operable communication with the inverting amplifier and is configured to control sample timing of a correlated offset signal. The second switch is in operable communication with the image sensing device and is configured to control sample timing of the image signal.

In a further embodiment, the image sensing device comprises a photodiode. In other embodiments, the inverting amplifier comprises a either a common source NMOS transistor or a common source PMOS transistor. In another embodiment, the first capacitor comprises a device that is formed at least in part using a Metal-Insulator-Metal (MiM) capacitance.

In a further embodiment, the CDS pixel comprises In another embodiment, a third switch operably connected to the inverting amplifier as a virtual short between its inverting input and its output, wherein the virtual short is configured to help control integration time. In a still further embodiment, the CDS pixel further comprises a fourth switch operably connected to the output of the inverting amplifier, the fourth switch configured to enable one or both of the first CDS pixel and a plurality of second CDS pixels to output onto an open drain output bus.

In another embodiment of the CDS pixel, the charge is first accumulated by the image sensing device before being transferred to the first capacitor. In another embodiment, the image sensing device further comprises a second capacitor constructed and arranged to increase a charge capacity of the image sensing device. For example, in one embodiment the second capacitor is connected in parallel with the image sensing device.

In a still further embodiment of the CDS pixel, the image sensing device is fabricated on a monolithic wafer and wherein the inverting amplifier is also fabricated on the same monolithic wafer as the image sensing device. In another embodiment, the image sensing device is fabricated separately from the inverting amplifier, wherein the image sensing device is configured to be on top of a monolithic wafer that has been fabricated using MEMS technology. In a still further embodiment, the image sensing device is configured to be fabricated on a separate wafer from the inverting amplifier and first capacitor, wherein the separate wafer on which the image sensing device is fabricated is hybridized to the CDS wafer. In yet another embodiment, the image sensing device is configured to be fabricated on a first wafer, the inverting amplifier and first capacitor are fabricated on a second wafer, and the first and second wafers are hybridized into a first focal plane array (FPA).

In another embodiment, the inverting amplifier and first capacitor are configured as a capacitive trans-impedance amplifier (CTIA). For example, in one embodiment, the first and second switches are configured to time the correlated offset signal and image signal so that the CTIA operates as a CDS CTIA, wherein the first capacitor is configured to store the offset signal during a first time period and to store the image signal during a second time period.

In another aspect, a method for sensing an image is provided. A correlated double sampled (CDS) pixel is provided, the CDS pixel in operable communication with an output bus. the CDS pixel comprising an image sensing device, and inverting amplifier, a first capacitor, a first switch, and a second switch. The image sensing device generates charge based on image content. The inverting amplifier is in operable communication with an output of the image sensing device, where the inverting amplifier comprises an inverting input and an amplifier output. The first is configured as a feedback to the inverting input of the inverting amplifier, where the first capacitor is configured as a switching capacitor and is configured to integrate an image signal received by the image sensing device. The first switch is in operable communication with the inverting amplifier and is configured to control sample timing of a correlated offset signal. The second switch is in operable communication with the image sensing device and is configured to control sample timing of the image signal.

A voltage across the image sensing device is set to a first predetermined value. A voltage across the first capacitor is initialized to a second predetermined value. The CDS output pixel is disconnected from the output bus. Charge is accumulated on the image sensing device, the charge related to a detected image intensity. The second predetermined value of voltage across the first capacitor is correlated to a virtual short at the input of the inverting amplifier. The CDS pixel output is reconnected to the output bus. The image sensing device is coupled to the inverting input of the inverting amplifier, wherein the coupling combines, at the inverting input of the inverting amplifier, the stored charge from the image sensing device with the correlated voltage across the first capacitor, so as to transfer enough charge from the image sensing device to return the image sensing device to the first predetermined value.

In a further embodiment, the inverting amplifier and first capacitor are configured as a capacitive trans-impedance amplifier (CTIA), In a still further embodiment, the first and second switches are configured to time the correlated offset signal and image signal so that the CTIA operates as a CDS CTIA, wherein the first capacitor is configured to store the offset signal during a first time period and to store the image signal during a second time period. In yet another embodiment, the first capacitor is operably coupled to the image sensing device a plurality of times during the time when the image sensing device is accumulating charge, and an integration time is defined as the time from when the image sensing device to is returned to the first predetermined value to the time an image signal voltage is read.

Details relating to this and other embodiments are described more fully herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and aspects of the disclosed embodiments will be more fully understood in conjunction with the following detailed description and accompanying drawings, wherein:

FIG. 1 is a general block diagram of a prior art amplifier circuit;

FIG. 2 is a block diagram of a first embodiment of an amplifier circuit;

FIG. 3 is a timing diagram showing the control signals and phases for multiple CDS pixel rows on a single column output bus, for the first embodiment of FIG. 2;

FIG. 4 is a block diagram of a second embodiment using NMOS devices and replacing the differential amplifier of FIG. 2 with a common source amplifier; and

FIG. 5 is a block diagram of a third embodiment using PMOS devices and replacing the differential amplifier of FIG. 2 with a common source amplifier;

In the drawings, like reference numbers indicate like elements, and like or related elements will have like or related alpha, numeric or alphanumeric designators.

DETAILED DESCRIPTION

Embodiments described herein include, but are not limited to, systems, methods, apparatuses, and articles of manufacture that relate to the design of sense amplifiers and related applications which may benefit from the use of Correlated Double Sampling (CDS) to minimize, or at least reduce, noise and offset variations and to increase signal power gain of the system, method, and/or apparatus. Embodiments of the sense amplifier systems, methods, and apparatuses have numerous applications, including, but not limited to, photodiode (Si, Ge, InGaAs, SLS) pixel arrays, Focal Plane Arrays (FPA), CCD imagers, active CMOS imagers, capacitive touch sensors, micro-bolometer, and related applications. At least some embodiments of the sense amplifier described herein further include embodiments that receive an analog current or charge signal as an input and provide an analog voltage signal to an external load.

Embodiments which use a similar process technology for fabrication of the image sensing device and the sense amplifier Read-Out IC (ROIC) are, in at least some embodiments, fabricated either as a monolithic device or on two wafers which are hybridized into one focal plane array (FPA). Hybridization often involves adding “bumps” to the wafers, flipping the image sensing wafer and bonding the wafers together. The flipped image sensing wafer is used in a “Back side” image collection mode. In some embodiments, the base wafers are made using the same process technologies. In some embodiments, the base wafers are made using process technologies. Other embodiments use a MEMS process to add image sensing devices, such as micro-bolometers, to the top side of the ROIC.

FIG. 2 is a block diagram of an amplifier circuit 50 in accordance with a first embodiment. Each pixel in a row has its own corresponding amplifier circuit 50; reference to the first amplifier circuit is made by referring to it amplifier circuit AMP 50(1), with each component in the AMP 50(1) similarly identified, e.g., photodiode 1 PD(1). The amplifier circuit 50(1) includes a photodiode (PD(1) 52; a transfer gate (TG) switch TG(1) 54, a common source (CS) amplifier CDS AMP(1) 56, a feedback capacitor CAP(1) 58, a sample and hold reset (SHR) switch SHR(1) 60, a sample and hold switch (SHS) SHS(1) 62, a row select switch (Rsel(1)) 64, and a reset (RST) switch RST(1) 74. The AMP(1) 50 circuit is connected to a common source of bias voltage Vbias 66, a source of threshold voltage (Vth(1)) 76, and a common Ibias output load 70, and a source of dark voltage Vdark 72. The amplifier circuit 50 provides an output voltage Vout 68.

In one embodiment, SHS(1) 62 is in operable communication with CDS AMP(1) 56 and is configured to control sample timing of a correlated offset signal. In one embodiment, TG(1) 54 is in operable communication with the PD(1) 52 (or any other image sensing device) and the inverting input of CDS AMP(1) 56, and is configured to control sample timing of an image signal. RST(1) 74 is configured to reset the CAP(1) 58 by creating a “virtual short” across CDS AMP(1) 56, thereby helping to contribute towards the control of integration time. RSEL(1) 64 is operably connected to the output of CDS AMP (1) 56 and is configured to enable the CDS pixel 50 (or even other CDS pixels) to output onto the output bus to Vout 68.

Referring to FIG. 2 (which is a block diagram of a correlated double sampled (CDS) pixel 50), described further below, at least some embodiments described herein help address the offset and noise error sources introduced by the SF 22 (of FIG. 1) by replacing the SF 22 with a Capacitive Trans-Impedance Amplifier (CTIA) 59. CTIAs can be formed with an inverting amplifier (e.g., CDS amplifier 56 of FIG. 2) plus a capacitor feedback element 58. By careful selection of timing signals, it is possible to convert a simple CTIA into a CDS CTIA using a single capacitor to store the offset and the signal, much like a chopper stabilized gain amplifier. This correlation occurs in the pixel at the interface between the PD 52 and the input (Vin) to the output CDS amplifier 56. This is different than the 4T pixel of FIG. 1, which requires a separate sample capacitor(s) and CDS amplifier after the SF 22 at the output of the column bus.

As shown in the exemplary embodiment of FIG. 2, a single transistor Common Source (CS) amplifier 56 replaces the source follower (SF) 22 of FIG. 1 and forms the CDS inverting amplifier 56 required for the CTIA. Note that the exemplary embodiment of FIG. 2 is intended to represent a general configuration of a CDS pixel 50, and is not limited to implementations that use only common source amplifiers as the amplifier 56, as will be appreciated. The specific type of amplifier used for the amplifier 56 is not important, although advantageously this amplifier should be an inverting amplifier (in contrast to a standard source follower (SF) amplifier, which is non-inverting).

Referring again to FIG. 2, the exemplary CDS amplifier 56 can be made using an NMOS transistor 80 (FIG. 4, described further herein) or a PMOS transistor (FIG. 5, described further herein). The capacitive feedback element 58 is, in one advantageous embodiment, fabricated using a Metal-Insulator-Metal (MIM) capacitor instead of the floating diffusion, but this is not limiting. The value of the capacitance 58 defines the input charge to output voltage gain of the CTIA. MOS switches are used to first sample a charge representing the offset voltage onto the MIM capacitor 58 during a reset phase. In the transfer phase, the PD 52 charge is transferred to the MIM capacitor 58 and the stored offset charge is subtracted from the output by the action of the CDS amplifier 56 in the CTIA. The output signal (minus offset and 1/f noise) Vout 68 is enabled onto the output bus by the series MOS switch 64. Note that, in FIG. 4, the output select switch is switch 82. In FIG. 5, the output select switch is the switch 156 that is coupled to RSEL 64.

Note that other embodiments of the amplifier circuit 50 are possible. For example, in one embodiment, the TG switch 54 can be eliminated if the application in which the amplifier circuit 50 is being used does not need to disrupt integration to provide a hold phase. In still another embodiment, the output enable switch (i.e., the Rsel switch 64) could be removed if the output does not need to be multiplexed onto a column bus. In still another embodiment, the Ibias output load 70 could be replicated per pixel or even moved into the pixel if sharing the bias is not required to multiplex the output or to reduce power consumption. Other variations will, of course, be apparent.

It will also be recognized that the photodiode (or other image sensing device) can be fabricated on the same or different monolithic wafer from the CDS AMP 56 (also referred to herein as CDS amp) and the various switches. In still further embodiments, some or all of the entire CDS pixel 50, including the photodiode and CDS AMP 56, are fabricated on the same CMOS wafer. In a still further embodiment, some or all of the entire CDS pixel 50 is fabricated on a strained layer superlattice (SLS) structure. In still further embodiments, the image sensing device is fabricated on a separate wafer from the inverting amplifier (e.g., CDS AMP 56) and feedback capacitor CAP(1) 58). Note that, in accordance with at least some embodiments, the TG(1) 54 switch can be configured to be on the same wafer as the image sensing device (e.g., PD(1) 52) or on the same wafer as the CDS AMP 56.

FIG. 3 is an exemplary timing diagram 100 showing the control signals for two rows of an [500×32] imager array using the block diagram of the amplifier circuit 50 of FIG. 2 and creates a “rolling shutter” with a frame rate of 60 FPS (33 us per row). This timing diagram is illustrative and not intended as limiting. The row length of 32 in the example timing diagram 100 assumes that the array is broken into groups of columns or “slices” for processing by an optional column concentration multiplexer. An illustrative example of a system and method usable for this type of processing is described in the commonly owned U.S. patent application Ser. No. 13/405,406, entitled IMAGER READOUT ARCHITECTURE UTILIZING A/D CONVERTERS (ADC) filed on Feb. 27, 2012, and published on Aug. 30, 2012 as publication number 20120218445, which is hereby incorporated by reference.

The integration time is controlled by how many rows (1 to 500) are accumulated, each row in the example of FIG. 3 corresponding to 33 us. The output sample is held by the integration capacitor 58 (FIG. 2), enabling a global shutter if desired. The hold time of the CDS 50 (FIG. 2) is limited by the leakage current at the input summing node of the amplifier, which may constrain the maximum useable hold time.

Again referring to FIG. 3, the first 33 us phase 102 performs a “hard” reset 104 where the PD(1) 52 voltage (and therefore charge) is initialized to a value determined by the unity gain behavior of the output amplifier 56(1)'s “virtual short” at its negative input Vin(1) (see FIG. 2) while the AMP(1) 50 is being loaded by the bias current Ibias 70. The CDS integration CAP(1) 58 voltage is initialized to the difference between the virtual short voltage (Vin (1) to CDS AMP(1) 56) and the desired zero input charge output voltage “Vdark” 72. Once TG(1) 54 is returned high, the PD(1) 52 can start accumulating charge based on incident photons and the output CDS AMP(1) 56 is disconnected from the bus (e.g., as shown in FIG. 3 by the pulse 104 at the start of the RSEL(1) signal.) In one embodiment, the accumulation of the PD(1) 52 during period 106 is (optionally) enhanced by additional capacitance (not shown in FIG. 2) added in parallel with the PD(1) 52. The signal is output to the column bus during period 108.

During the second 33 us phase 106, the PD(1) 52 continues to integrate while the subsequent PD(2) through PD(n) are being initialized (as determined by the respective RSel(2) through RSel(n) signals). While subsequent rows are initialized, any integrated charge on the respective CDS integration CAP(1) through CAP(n) is cleared based on the output voltage of the selected row (uncorrelated to its own row's amplifier).

During the third 33 us phase 108, the CDS AMP 56 is again connected to the bus and the CDS integration CAP(1) 58 is re-correlated to the virtual short at the input of the CDS AMP(1) 56 (by briefly closing switch SHR(1)) while loaded by the bias current Ibias 70. After this has settled, there is a non-overlapping period 110 followed by an output period 112 (designated in FIG. 3 as “output row 1”). To output the signal, the TG(1) switch 54 is closed which sums the PD(1) CAP 58 onto the input node of the CDS AMP(1) 56. By the operation of the inverting input (i.e., CDS AMP(1) 56), the output of AMP(1) 50 (i.e., Vout 68) output changes from the reset value to an output value which corresponds to transferring enough charge to the CDS integration CAP(1) 58 to cancel the accumulated charge of the PD(1) 52, returning the PD(1) 52 voltage back to its initialized value. The behavior of an amplifier with a current (moving charge) input and voltage output is often referred to as a Trans-Impedance Amplifier (TIA).

The linearity of the charge to voltage conversion is negatively affected by the non-linear parasitic of the integration CAP(1) 58. Advantageously, in at least some embodiments, a linear capacitor such as Metal-Insulator-Metal (MIM) or a metal Finger capacitor is used. In at least some other embodiments, voltage coefficients are reduced by using larger series capacitors, such as by replacing CAP(1) 58 with two capacitors in series, e.g., CAP(1 a) 58 a and CAP(2 b) 58 b (not shown).

Referring again to FIGS., 2 and 3, after the charge transfer is complete, the PD(1) 52 can be disconnected from the CDS AMP(1) 56 to prevent further integration of incident photons. Since the CDS integration CAP(1) 58 was initialized to the difference between the virtual short value and the desired Vdark(1) 72 output, that amount of charge is already on the CAP(1) 58, and is effectively subtracted from the required charge to cancel the PD(1) 52 charge—effecting a correlation to the output amplifier input offset and noise. The CDS CAP(1) 58 also enables sample and hold behavior where the hold time is limited by the total leakage current at the input summing node of the amplifier. In further embodiments, each CDS (column) output is read in parallel or is further multiplexed down to increase the effective column pitch.

The last 32 us of the 33 us phase 114 are used, in one embodiment, for a 32:1 column multiplexer timing where the inherent hold of the CDS pixel allows 1 us for each of the 32 columns to drive a single open drain serial output bus. Alternately, in another embodiment, the same 32 columns drive 32 sample and hold circuits in a Read Out IC (ROIC) (not shown in the Figures, but described, for example, in the aforementioned, incorporated by reference U.S. Patent Publication US-2012-0218445-A1) which are multiplexed to create the serial sampled data stream. Illustrative examples of ROICs usable with at least some embodiments are described the aforementioned and incorporated by reference co-pending Ser. No. 13/405,406 patent application, as well as in commonly assigned and co-pending nonprovisional application Ser. No. 14/490,448, entitled “Foveal Imager ROIC,” and filed on Sep. 18, 2014, which is likewise incorporated by reference.

The fourth 33 us phase 114 of FIG. 3 shows how the second row of CDS pixels are selected to drive the common column bus (either per column or group of columns with CDS output multiplexer). During this phase, the first row is in an idle state. Integration of the PD(2) could be occurring since TG(1) is not active and the PD(1) has been returned to its initial value. In one embodiment, this configuration is used only in extreme low light situations where the integration time was the entire frame time, but that is not limiting. In some instances, there is a sequence of soft resets (correlated to a group of rows or columns per bias current) to clear charge accumulated over the past line both on the CDS integration capacitor 58 and the PD 52. The actual integration cycle is initialized by a hard reset, as per the first 33 us phase where the output loading of the amplifier is identical to the environment it will see when the correlation and sample occur (one amplifier per bias current). Note that each pixel (column) of each row has its own PD. The first and second row, in at least some embodiments, can be in different modes. In one embodiment, if the integration time is at its maximum, there may never be a hard reset where only the single row is reset. Note that, a soft reset is where multiple rows are reset simultaneously, but this can, in some instances, be less accurate

In another embodiment, the CDS pixel acts as a Capacitive Trans-Impedance Amplifier (CTIA). This is, for example, beneficial if the PD 52 has minimal charge accumulation capacity. In this embodiment, the integrating cap 58 is connected to the PD 52 a plurality of times during the image accumulation phase and the charge is accumulated on the integration capacitor 58. The image integration time is now defined as the time from the last reset to the time the image signal voltage is read.

It will also be appreciated that the circuit of FIG. 2 and timing of FIG. 3 each have numerous applications and are not limited to the particular applications described in connection with FIGS. 2 and 3.

Referring to FIGS. 4 and 5, the differential amplifier of FIG. 2 (i.e., the CDS AMP 56) in one embodiment, is replaced with a common source amplifier (e.g., the NMOS M1 amplifier 80 of FIG. 4 NMOS, or the PMOS amplifier 145 of FIG. 5. For example, FIG. 4 is a block diagram showing one illustrative embodiment of an NMOS CDS pixel. FIG. 5 is a block diagram showing one illustrative embodiment of a 6T PMOS CDS pixel.

It is envisioned that the embodiments described herein also could be combined with some or all of the technologies described in the commonly assigned U.S. Pat. No. 7,215,270, entitled “Sigma-Delta Modulator having selectable OSR with Optimal Resonator Coefficient,”; U.S. Pat. No. 7,576,671, entitled “Mismatch-shaping Dynamic Element Matching Systems and Methods for Multi-bit Sigma-delta Data Converters,”; U.S. Pat. No. 7,605,652, entitled “Sigma-delta Based Class D Audio Power Amplifier with High Power Efficiency,”; U.S. Pat. No. 7,612,608, entitled “Sigma-delta Based Class D Audio or Servo Power Amplifier with Load Noise Shaping,”; U.S. Pat. No. 7,860,189, entitled “Hybrid Heterodyne Transmitters and Receivers,” U.S. Pat. No. 8,379,760, entitled “Hybrid Heterodyne Transmitters and Receivers,” U.S. Patent Publication US-2012-0218445-A1, entitled “Imager Readout Architecture Utilizing A/D Converters,” the provisional patent application entitled Foveal Imager Readout Integrated Circuit (ROIC), application Ser. No. 61/879,276, by Eugene M. Petilli, filed on Sep. 18, 2013 and converted to a nonprovisional patent application having Ser. No. 14/490,448 and attorney docket number INTRI-028AUS on Sep. 18, 2014; and, and the provisional patent application entitled “Stacked Photodiode Multispectral Imager, application Ser. No. 61/902,912, by Eugene M. Petilli, filed on Nov. 12, 2013 and converted to a nonprovisional patent application having Ser. No. 14/539,607 and attorney docket number INTRI-029AUS on Nov. 12, 2014. The contents of each of these above-listed patents and patent applications are hereby incorporated by reference in their entirety.

Throughout the present disclosure, absent a clear indication to the contrary from the context, it should be understood individual circuit elements as described may be singular or plural in number. For example, the terms “circuit” and “circuitry” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together to provide the described function. Additionally, the term “signal” may refer to one or more currents, one or more voltages, or a data signal. Within the drawings, like or related elements have like or related alpha, numeric or alphanumeric designators. Further, while at least some of the embodiments described herein have been discussed in the context of implementations using discrete electronic circuitry (preferably in the form of one or more integrated circuit chips), the functions of any part of such circuitry may alternatively be implemented using one or more appropriately programmed processors, depending upon the signal frequencies or data rates to be processed.

Similarly, in addition, in the Figures of this application, in some instances, a plurality of system elements may be shown as illustrative of a particular system element, and a single system element or may be shown as illustrative of a plurality of particular system elements. It should be understood that showing a plurality of a particular element is not intended to imply that a system or method implemented in accordance with the embodiments described herein, or the claims, must comprise more than one of that element, nor is it intended by illustrating a single element that the embodiments described herein, or the claims, are limited to embodiments having only a single one of that respective elements. In addition, the total number of elements shown for a particular system element is not intended to be limiting; those skilled in the art can recognize that the number of a particular system element can, in some instances, be selected to accommodate the particular user needs.

In describing the embodiments illustrated in the figures, specific terminology (e.g., language, phrases, etc.) may be used for the sake of clarity. These names are provided by way of example only and are not limiting. The described embodiments and listed claims are not limited to the specific terminology so selected, and each specific term at least includes all grammatical, literal, scientific, technical, and functional equivalents, as well as anything else that operates in a similar manner to accomplish a similar purpose. Furthermore, in the illustrations, Figures, and text, specific names may be given to specific features, processes, military programs, etc. Such terminology used herein, however, is for the purpose of description and not limitation.

Although the embodiments disclosed herein have been described and pictured in a preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form, has been made only by way of example, and that numerous changes in the details of construction and combination and arrangement of parts may be made without departing from the spirit and scope of the embodiments and claims provided herein. Those of ordinary skill in the art will appreciate that the embodiments described herein can be modified to accommodate and/or comply with changes and improvements in the applicable technology and standards referred to herein. Variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the embodiments and claims provided herein. In addition, the technology disclosed herein can be used in combination with other technologies. Accordingly, the foregoing description is by way of example only and is not intended as limiting. In addition, all publications and references cited herein are expressly incorporated herein by reference in their entirety.

Having described and illustrated the principles of the technology with reference to specific implementations, it will be recognized that the technology can be implemented in many other, different, forms, and in many different environments. Having described the preferred embodiments, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. These embodiments should not be limited to the disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims. The scope is defined in the following claims and the equivalents thereto. 

1. A first Correlated Double Sampled (CDS) pixel comprising: an image sensing device which generates charge based on image content; an inverting amplifier in operable communication with an output of the image sensing device, the inverting amplifier comprising an inverting input and an amplifier output; a first capacitor configured as a feedback to the inverting input of the inverting amplifier, the first capacitor configured as a switching capacitor and configured to integrate an image signal received by the image sensing device; a first switch in operable communication with the inverting amplifier, the first switch configured to control sample timing of a correlated offset signal; and a second switch in operable communication with the image sensing device, the second switch configured to control sample timing of the image signal.
 2. The first CDS pixel of claim 1, wherein the image sensing device comprises a photodiode.
 3. The first CDS pixel of claim 1, wherein the inverting amplifier comprises a common source NMOS transistor.
 4. The first CDS pixel of claim 1, wherein the inverting amplifier comprises a common source PMOS transistor.
 5. The first CDS pixel of claim 1, wherein the first capacitor comprises a device that is formed at least in part using a Metal-Insulator-Metal (MiM) capacitance.
 6. The first CDS pixel of claim 1, wherein the first capacitor comprises a device that is formed at least in part using a Metal Finger capacitance.
 7. The first CDS pixel of claim 1, further comprising a third switch operably connected to the inverting amplifier as a virtual short between its inverting input and its output, wherein the virtual short is configured to help control integration time.
 8. The first CDS pixel of claim 1, further comprising a fourth switch operably connected to the output of the inverting amplifier, the fourth switch configured to enable one or both of the first CDS pixel and a plurality of second CDS pixels to output onto an open drain output bus.
 9. The first CDS pixel of claim 1, wherein the charge is first accumulated by the image sensing device before being transferred to the first capacitor.
 10. The first CDS pixel of claim 9, wherein the image sensing device further comprises a second capacitor constructed and arranged to increase a charge capacity of the image sensing device.
 11. The CDS pixel of claim 10, wherein the second capacitor is connected in parallel with the image sensing device.
 12. The CDS pixel of claim 1, wherein the image sensing device is fabricated on a monolithic wafer and wherein the inverting amplifier is also fabricated on the same monolithic wafer as the image sensing device.
 13. The CDS pixel of claim 1, wherein the image sensing device is fabricated separately from the inverting amplifier, wherein the image sensing device is configured to be on top of a monolithic wafer that has been fabricated using MEMS technology.
 14. The CDS pixel of claim 1, wherein the image sensing device is configured to be fabricated on a separate wafer from the inverting amplifier and first capacitor, wherein the separate wafer on which the image sensing device is fabricated is hybridized to the CDS wafer.
 15. The CDS pixel of claim 1, wherein the image sensing device is configured to be fabricated on a first wafer, the inverting amplifier and first capacitor are fabricated on a second wafer, and the first and second wafers are hybridized into a first focal plane array (FPA).
 16. The CDS pixel of claim 1, wherein the inverting amplifier and first capacitor are configured as a capacitive trans-impedance amplifier (CTIA).
 17. The CDS pixel of claim 16, wherein the first and second switches are configured to time the correlated offset signal and image signal so that the CTIA operates as a CDS CTIA, wherein the first capacitor is configured to store the offset signal during a first time period and to store the image signal during a second time period.
 18. A method for sensing an image, the method comprising: providing a correlated double sampled (CDS) pixel in operable communication with an output bus, the CDS pixel comprising: an image sensing device which generates charge based on image content; an inverting amplifier in operable communication with an output of the image sensing device, the inverting amplifier comprising an inverting input and an amplifier output, the amplifier output corresponding to the CDS pixel output; a first capacitor configured as a feedback to the inverting input of the inverting amplifier, the first capacitor configured as a switching capacitor and configured to integrate an image signal received by the image sensing device; a first switch in operable communication with the inverting amplifier, the first switch configured to control sample timing of a correlated offset signal; and a second switch in operable communication with the image sensing device, the second switch configured to control sample timing of the image signal; setting a voltage across the image sensing device to a first predetermined value; initializing a voltage across the first capacitor to a second predetermined value; disconnecting the CDS pixel output from the output bus; accumulating charge on the image sensing device, the charge related to a detected image intensity; correlating the second predetermined value of voltage across the first capacitor to a virtual short at the input of the inverting amplifier; reconnecting the CDS pixel output to the output bus; and coupling the image sensing device to the inverting input of the inverting amplifier, wherein the coupling combines, at the inverting input of the inverting amplifier, the stored charge from the image sensing device with the correlated voltage across the first capacitor, so as to transfer enough charge from the image sensing device to return the image sensing device to the first predetermined value.
 19. The method of claim 18, further comprising: configuring the inverting amplifier and first capacitor as a capacitive trans-impedance amplifier (CTIA); and configuring the first and second switches to time the correlated offset signal and image signal so that the CTIA operates as a CDS CTIA, wherein the first capacitor is configured to store the offset signal during a first time period and to store the image signal during a second time period.
 20. The method of claim 18, further comprising: operably coupling the first capacitor to the image sensing device a plurality of times during the time when the image sensing device is accumulating charge; and defining an image integration time as the time from when the image sensing device to is returned to the first predetermined value to the time an image signal voltage is read. 